The rather common mixed companion planting that associates trees with grass crops, especially in the past, is based on the reciprocal benefits that the crops involved can draw from this situation. Trees both constitute a wind-breaking barrier for the grasses, and can offer a further source of income in plots of land not used by grass crops. Companion planting is based on the principle whereby many plant species, including crops, derive benefits if grown in more complex agro-ecosystems. The plants most commonly used for this purpose have traditionally been vines and olive trees associated with fodder.
